Which is the x value and which is the y value

When data is presented in a table like this, the x-value (independent variable) is usually the one on the left.

The y-value (dependent variable) is usually the one on the right. (This is the assumption made by spreadsheet programs that do graphing.)

_____

The slope of the graph is the difference of a pair of y-values divided by the difference of the corresponding pair of x-values. These graphs both include the point (0, 0), so you can draw the graph once you know the slope.

39) ∆y/∆x = (4.5 -3)/(3 -2) = 1.5/1 = 1.5 . . . . the slope of the line

... y = 1.5x . . . . . the equation of the line

... y = 1.5×25 = 37.5 . . . . the height of 25 pieces (inches)

40) ∆y/∆x = (474 -237)/(6 -3) = 237/3 = 79 . . . . . the slope of the line

... y = 79x . . . . . the equation of the line

... y = 79×30 = 2370 . . . . the cost for 30 nights (dollars)